Confirming that most Covid rules in England will be lifted on 19 July, Health Secretary Sajid Javid encouraged event organisers to require attendees to show so-called vaccine passports.
They are available through the NHS app and also show if a person has natural immunity after contracting the disease.
But the guidance is not mandatory.
Therefore organisers would not be legally required to follow it.
Speaking at a Downing Street press conference, Boris Johnson said: "As a matter of social responsibility we're urging nightclubs and other venues with large crowds to make use of the NHS Covid pass, which shows proof of vaccination, a recent negative test or natural immunity as a means of entry."
In written guidance published after the press conference, the government said it "reserves the right" to force venues to require people to show their vaccine passport in order to be allowed in.
How can I get a vaccine passport?
People in England can do this by requesting an NHS Covid Pass via the NHS website or the NHS app.
Once logged in an NHS Covid Pass can be requested. The system generates a QR code, which lasts for 28 days.
An NHS Covid Pass can be obtained two weeks after a second dose of the Covid vaccine, as long as both doses were given in England.
A pass can be requested if you've had a negative PCR test or lateral flow test result within the past 48 hours, which you have reported on the NHS website. These passes last 48 hours after the test result.
Alternatively, a pass can be given following a positive PCR test result within the last six months, and have finished self-isolating. The pass lasts for 180 days after the test result.
People who have had both their jabs can also request an NHS Covid Pass letter by calling 119. This only shows vaccination status and has no expiry date.
However, the move has received push back from bar and club owners.
Alex Proud, owner of Proud nightclubs, said: "I find it deeply worrying and frustrating because it's discriminatory against younger people who are less likely to have been able to have the vaccinations."
"We emphasise that we've invested in sanitation and we feel these measures are adequate rather than overly authoritarian Covid passports," he told the BBC.
Michael Kill, who runs the Night Time Industries Association, said: "We have consistently opposed the use of Covid passports for access to industry events and venues, logistically it presents many issues, supported by the recent Covid status certificate report administered by government, steering us clear from the use of this method to mitigate risk."
But Mr Johnson warned that the "pandemic is not over" as he outlined what he described as a "cautious approach" to relaxing restrictions.
"If we're cautious and everybody gets vaccinated, then, yes, we can make steady progress."
The decision to relax restrictions comes as UK case numbers have increased to an average of 30,000 a day, driven by the highly-transmissible Delta variant of the disease.
The variant has caused a surge in cases across Europe where other nations have decided to reintroduce restrictions.
In the Netherlands, the Dutch government re-imposed curbs on nightclubs, music festivals and restaurants on Friday while Spain's Canary Islands have asked the government to bring back curfews.